Variable efficiency mechanical transmission

ABSTRACT

A variable efficiency thread-type nut for use with a screw having a helical thread, the nut comprising a body having a through bore to receive the screw, a roller carried by the nut body and extending into the bore thereof so as to engage the screw thread, bearing means mounting the roller for turning movement and also for movement between advanced and retracted positions in the nut body, and yieldable means for biasing the roller to its advanced position and into engagement with the thread of the screw, as well as a thread means comprising one or more elements or shoulders rigidly carried in the bore of the nut body and engageable with a part of the screw thread. The thread elements or shoulders are normally out of engagement with the screw thread at such time as the axial loading between the screw and the nut is less than a predetermined level. Under these circumstances, the roller remains biased to its advanced, threadengaging position. When the load exceeds the predetermined level, the biasing means enables the roller to yield under the load and thus shift to a retracted position whereupon the rigid shoulder or thread of the nut body frictionally engages the screw thread and effects an increased drag therewith, thus tending to retard relative (usually retrograde) turning between the nut body and screw. Upon removal of the heavy load, the roller again assumes its advanced, thread-engaging position and the shoulder becomes disengaged from the screw threads, thus enabling the nut and screw to undergo the normal, especially free relative turning movement.

[ 1! Oct. 23, 1973 VARIABLE EFFICIENCY MECHANICAL TRANSMISSION [75]Inventor: John C. Kennedy, Georgetown,

Conn.

[73] Assignee: N0rc0,Inc.,Town ofRidgefield,

Fairfield, Conn.

[22 Filed: June 36,1952

21 Appl. No.: 268,058

Primary Examiner-Leonard H. Gerin Attorney-H. Gibner Lehmann et al.

[57] ABSTRACT A variable efficiency thread-type nut for use with a screwhaving a helical thread, the nut comprising a body having a through boreto receive the screw, a roller carried by the nut body and extendinginto the bore thereof so as to engage the screw thread, bearing meansmounting the roller for turning movement and also for movement betweenadvanced and retracted positions in the nut body, and yieldable meansfor biasing the roller to its advanced position and into engagement withthe thread of the screw, as well as a thread means comprising one ormore elements or shoulders rigidly carried in the bore of the nut bodyand engageable with a part of the screw thread. The thread elements orshoulders are normally out of engagement with the screw thread at suchtime as the axial loading between the screw and the nut is less than apredetermined level. Under these circumstances, the roller remainsbiased to its advanced, thread-engaging position. When the load exceedsthe predetermined level, the biasing means enables the roller to yieldunder the load and thus shift to a retracted position whereupon therigid shoulder or thread of the nut body frictionallly engages the screwthread and effects an increased drag therewith, thus tending to retardrelative (usually retrograde) turning between the nut body and screw.Upon removal of the heavy load, the roller again assumes its advanced,thread-engaging position and the shoulder becomes disengaged from thescrew threads, thus enabling the nut and screw to undergo the normal,especially free relative turning movement.

10 Claims, 10 Drawing Figures PATENTEUHBT 23 I975 VARIABLE EFFICIENCYMECHANICAL TRANSMISSION This invention relates generally to specialtypes of mechanical transmissions involving screw elements, and moreparticularly to transmissions wherein a screw having a helical thread isassociated with a nut provided with an anti-friction roller adapted forengagement with the screw thread. In the past a large number ofdifferent types of power transmission devices involving screws have beenproposed and constructed. In cases where it was desired to retardrelative turning movement between a screw and a thread-engaging nut,some type of pawl and ratchet arrangement was frequently employed; forexample, a stationary screw could be engaged by a rotating nut, with thelatter carrying a ratchet arranged to be cooperable with a pawl that isfixed with respect to the screw. The nut could be turned or advanced toa desired position, after which any rotation of the nut in the oppositedirection was inhibited by the ratchet and pawl until the latter wasmanually released.

Other types of locking arrangements for nuts included the well-knownback-to-back locking nut arrangement, wherein one nut was tightenedagainst another to prevent relative turning movement of the nut andscrew. Also, in the past, nuts having set screws to engage flat portionsof a cooperable screw have frequently been employed to effect lockingthereof onto the screw once a predetermined relative position wasattained. While in general the locking arrangements described aboveoperated satisfactorily for their specific purposes, the range ofusefulness was often limited in that the locking or unlocking operationrequired additional tools (such as wrenches) or an additional manualoperation (such as manually releasing a pawl.) In cases where there wasinadequate space to easily effect such a locking and unlockingoperation, the required activity was often cumbersome or awkward toperform, and frequently the tools required were not readily at hand.

SUMMARY The above disadvantages and drawbacks of prior locking,back-check and similar mechanical transmissions of the type noted areobviated by the present invention which has for one object the provisionof a novel and improved variable efficiency type locking transmissionwhich is especially simple in its construction, reliable in operation,and which operates automatically to effect its locking or unlocking inresponse to the application and removal of heavy, axially loads appliedthereto.

The above object is accomplished by a novel variable-efficiency type nutfor a screw having a helical thread, said nut comprising an annular bodyadapted to travel along the length of the screw, and a roller carried bythe nut body and normally engaging the thread of the screw, inconjunction with bearing means which mounts the roller not only forturning movement about its axis but also for axial movement betweenadvanced and retracted positions with respect to its mounting. Yieldablemeans are provided for biasing the roller to its advanced position tonormally maintain its engagement with the thread of the screw, and atleast one shoulder or thread element is rigidly carried in the nut bodyand is normally out of engagement with the screw thread when the rolleris in its advanced position. The

biasing means enables theroller to yield and shift to its retractedposition in response to heavy loading be tween the nut and the screw,such that the thread element or shoulder frictionally engages the screwthread to effect an increased drag therewith, which tends to retardrelative turning movement between the nut body and screw. Upon removalof the heavy load, the roller assumes its advanced, thread-engagingposition once again whereby the shoulder of the nut becomes disengagedfrom the screw threads, enabling the nut and screw to undergo freerelative turning movement once again.

Other features and advantages will hereinafter appear.

In the accompanying drawings, illustrating one embodiment of theinvention:

FIG. 1 is alongitudinal section of a variable efficiency transmission asprovided by the present invention.

FIG. 2 is a left end elevational view of the nut part of FIG. 1.

FIG. 3 is a right end elevational view of the nut part of FIG. 1,

FIG. 4 is a top plan view of the nut part.

FIG. 5 isa development of the nut part of FIG. 3 illustrating therelative locations of the rollers with respect to the nut body.

FIG. 6 is a fragmentary longitudinal section ofthe variable efficiencynut and helical thread screw illustrating the engagement of the screwthread by the thread elements or shoulders when the roller means areurged to the retracted position by heavy loading applied between the nutand screw.

FIG. 7 is a fragmentary longitudinal section of the variable efficiencynut and helical thread screw illustrating the clearance space betweenthe nut threads and the screw threads when the roller is in itsadvanced, threadengaging position.

FIG. 8 is a front elevational view of an adjustable platform employingthe variable efficiency transmission of the present invention, theplatform being adapted to support articles or merchandise above a flatsurface such as a trailer truck flat bed. FIG. 9 is a-right'endelevational view of the platform of FIG. 8, illustrating two of thevariable efficiency invention supporting the transmissions of thepresent same. i r i FIG. 10 is a top plan view of the platform of FIGS.8 and 9 illustrating an interconnecting chain for effecting simultaneousturning of the novelxnuts of the present invention, as employedtherewith.

Referring first to FIG. 1 thereis illustrated amechanical transmissiongenerally designated by the numeral 10, including a screw 12 having aspiral thread comprising a crest l4 and groove 16, and including a nut17 comprising an annular nut body or follower member 18 having aninternal thread or crest 20 and groove 22, the thread 20 being adaptedto mate with the screw thread 14. The nut illustrated in FIGS. 2-4 has athrough bore 24 to receive the screw, and has a centralizing bushing 26disposed at one end thereof, the bushing being press fitted into thebore 24 and centralizing the screw with respect to the nut. A threadedprojecting hub 28, disposed at one end of the nut body, provides meansfor securing the nut to a plate or bracket with suitable hardware (notshown).

In accordance with the present invention, the mating threads 14 and 20of the screw and nut respectively, are constituted as to provideclearance spaces therebetween, such that the screw 12 if properlypositioned can physically occupy the bore 24 of the nut without contactbetween the threads. The thread 20 is seen to constitute a shoulderwhich is rigidly carried in the bore 24 of the nut body 18 and which isengageable with the thread 14 of the screw 12. Further, by the presentinvention there is provided a plurality of rollers 28, 30 and 32, asillustrated in FIG. 3, the rollers being carried on the nut body 18 andextending radially into the bore 24 thereof so as to be engageable withthe screw thread 14. The relative locations of the rollers with respectto the nut body 18 are illustrated in the FIG. development of the nut.The rollers 28, 30 and 32 are carried on anti-friction bearings 34, 36and 38 respectively, one of which is illustrated in FIGS. 6 and 7, theantifriction bearings enabling free turning movement of the rollersabout their respective axes. It is to be noted that the rollers 28, 30and 32 are of substantially identical configuration, and the same istrue with respect to the bearings34, 36 and 38.

Referring to FIG. 6, the roller 28 and anti-friction bearing 34constitute a cartridge and are carried in a housing 40 which is disposedin a radially extending hole 42 in the nut body 18. The cartridgehousing 40 is held captive in the hole 42 by a retainer washer 44received in a groove 46 of the wall thereof, as illustrated.

As seen in FIGS. 6 and 7, the roller 28 is provided with a transversegroove 48 in which there is received a split washer 50. In addition, athrust bearing comprising a sleeve 52 and ball-bearing 54 is disposed atthe innermost end of the cartridge adjacent the non-threadengaging endof the roller 28. A pair of back-to-back spring washers 56, 58 engagethe washer 50 and the sleeve 52. It should be noted that the roller 28is of slightly smaller diameter than both the inner race of the needlebearing 34 and the inner wall of the sleeve 52, such that the roller 48can undergo limited sliding movement in a direction parallel to itsaxis. By the above arrangement, the rolleris biased inwardly to theposition illustrated in FIG. 7, hereinafter referred to as the advancedposition. The bowed washers 56, 58 thus constitute yieldable meansbiasing the roller 28 into engagement with the thread 14 of the screw12.

The operation of the variable efficiency screw-type transmission of thepresent invention can now be readily understood by referring to FIGS. 6and 7. FIG. 7 illustrates the roller 28 biased to its advanced,threadengaging position by the spring washers 56 and 58. For thisposition the 'roller 28 and the rollers 30 and 32 are engaging thethread 14 of the screw 12 at such times that arelatively light'axialload is applied to the latter in the direction indicated by the arrow Ffrelative to the nut. Under this circumstance, as the nut and screwundergo relative rotation, the frictional drag therebetween is extremelysmall since the three rollers are the only portions of the nut engagingthe screw 12, and each is free to rotate during their engagement (withone wall of the groove 16). As illustrated in FIG. 7 there exists aspace between the crest l4 and walls of the groove 16 of the screw 12 onthe one hand, and the walls of the groove 22 and crest of the nut thread14 on the other hand, such that the screw occupies the bore 24 of thenut without contact between the cooperable or mating threads thereof.

Referring now to FIG. 6 it is seen that the roller 28 has a taperedconfiguration at its thread-engaging end 60. It will be understood thatwhen a force F applied in the direction indicated in FIG. 6 exceeds apredetermined amount, the thread 14 of the screw will tend to cam thetapered end 60 of the roller in a manner that the latter will be urgedradially outward to its retracted position, which is the positionillustrated in FIG. 6. This camming occurs against the action of thespring washers 56 and 58. As this happens it will be seen that thethread 20 of the nut and the thread 14 of the screw will be brought intoengagement with one another. This engagement occurs along virtually theentire length of the mating nut and screw threads, and as a result agreatly increased contact area therebetween is effected. By the abovearrangement, any tendency toward further relative turning movementbetween the nut and screw is inhibited by a greatly increased frictionaldrag force resulting from the sliding contact area. A beneficial usefulresult is thus realized, since the mechanism can now be adapted for useas an automatic back-check which responds to the application of a heavyload, by automatically locking itself with the parts in the relativepositions occupied at the time such a heavy load is applied. Uponremoval of the load, the spring washers 56 and 58 shift the roller 28 toits advanced position (FIG. 7) once again, wherein the nut and screw arefree to resume efficient, low-drag, relative turning movement. It willbe understood that in the presence of a heavy load, each of the rollers28, 30, 32 is urged to its retracted position, since the rollers are ofsubstantially identical configuration and the spring washers employedtherewith provide roughly equivalent biasing forces thereto,respectively.

A typical application for the novel variable efficiency transmission ofthe present invention is illustratd in FIGS. 8-10, wherein there isshown a vertically adjustable platform 62 for a trailer truck 64. Theplatform is substantially rectangular in shape and is supported by fourscrews 66, 68, and 72 respectively which are fixed and non-rotating. Theplatform has four brackets 74, 76, 78 and 80, two of which are disposedrespectively on opposite sides thereof, each of the brackets carrying avariable efficiency nut substantially identical to that illustrated inFIGS. 1-7, the four nuts being designated 82, 84, 86 and 88respectively. Eachof the nuts is rotatably mounted on its respectivebracket for turning movement. Also, there is associated with each nut asprocket wheel rigidly fastened thereto, the sprocket wheels beingdesignated by the numerals 90, 92, 94 and 96 respectively. A chain 98connects each of the sprocket wheels for effecting simultaneous turningmovement of each of the nuts 82-88 when any one thereof is turnablydriven. Guide pulleys for the chain 98, designated 100, 102, 104 and 106are carried respectively by the brackets 74, 76,78 and 80, asillustrated best in FIGS. 9 and 10. One of the nuts 84 is furtherprovided with a crank handle 101 to enable the four nuts to besimultaneously manually rotated in order to raise and lower theplatform.

The operation of the platform incorporating the variable efficiency nutof the present invention can be readily understood. It is to be notedthat the platform 62 is of such a weight, when unloaded, that therollers carried by the nuts supporting the platform remain biased totheir advanced positions (as in FIG. 7), wherein the load (due to theweight of the platform) is sustained entirely by the nut rollers and notby the nut thread 20. Under this circumstance, the threads 14 of thescrews possible without departing from the spirit of the invention.

I claim:

1. A variable effiency nut for a screw comprising, in

are out of engagement with the mating threads of 5 combination:

the nuts and the frictional drag therebetween is very low. Thus, theadjustment of the unloaded platform 62 to the desired position is easilyaccomplished by manual rotation of the crank handle 101. After thedesired position of the platform is attained, it can be loaded with themerchandise to be stored or shipped, such loading preferably beingaccomplished by a fork-lift (not shown) or by other mechanical means.The additional weight of the merchandise on the platform causes anappreciable additional load on the nuts 82, 84, 86 and 88, such that therollers thereof are all cammed radially outwardly to their retractedpositions, respectively (as in FIG. 6) whereby the threads of the nutsfrictionally engage the respective threads of the screws. Due to thelarge friction of contact between the respective nut and screw threads,the drag force therebetween is sufficient to oppose any further relativeturning. Thus the platform 62 remains fixed in the preset position untilthe merchandise is unloaded, at which time the rollers of the nutsresume their advanced positions respectively, thus enabling easy manualreadjustment of the platform position to a different elevation, ifdesired. It will be understood that the particular load applied to theplatform, at which the locking takes place, will depend upon thestiffness of the spring washers 56, 58 and also upon the number ofrollers carried by the nut. By employing washers having greaterstiffness, the platform can be made to sustain a heavier load prior tolocking. Also, the provision of additional rollers spaced about the nutbody willhave the same effect of increasing the load at which lockingoccurs.

There are a number of advantages in the above arrangement. Since theoperator of the crank handle is sometimes in an awkward position whileadjusting the platform, it is important that the force required toperform the adjustment be made minimal. By the present invention, themanual adjustment of the position of the unloaded platform is madeespecially easy by the provision of the anti-friction rollers engagingthe screw threads. In addition, the platform is automatically locked,inits pre-set position once it has been loaded, due to the weight of themerchandise. Thus, the operator need not operate any additional leversormechanism to effect such a locking operation. Finally, readjustment ofthe position of the platform to a different elevationis readilyaccomplished once the particular merchandise has been unloaded, thusproviding for extremely flexible operation. The above constructionrepresents an extremely safe mechanism, since the platform, when heavilyloaded, cannot descend of itsown accord. The load bearing capacity isdetermined by the strength of the cooperable threads on the nut and thescrew, and not upon that of the roller elements. As a result, thelikelihood of injury to personnel is virtually eliminated.

From the above it can be seen that I have provided a novel and improvedvariable efficiency transmission and nut which is extremely simple inconstruction and foolproof in operation. The device thus represents adistinct advance and improvement in mechanical transmission technology.Variations and modifications are a. an annular nut body having a throughbore to receive the screw,

b. a roller carried by said nut body and extending into the bore thereofso as to be engageable with the thread of the screw,

0. bearing means mounting the roller for turning movement about itsaxis, and for movement between advanced and retracted positions in thebody,

d. yieldable means biasing the roller to its advanced position forengagement with the thread of the screw, and

e. a shoulder rigidly carried in the bore of the nut body and engageablewith a part of the screw thread,

f. said shoulder being normally out of engagement with the screw threadwhen the roller is in its advanced position adapted to engage thethread,

g. said yieldable biasing means enabling the roller to yield and shiftto its retracted. position in response to heavy lateral loading thereonby the screw, such that the shoulder of the nut body frictionallyengages the screw thread and effects an increased drag therewith,thereby tending to retard relative turning between the nut body andscrew.

2. The invention as defined in claim 1, and further including:

a. a screw having a spiral thread with crests and grooves, i

b. said shoulder comprising a portion of a screw thread adapted to matewith the thread of said screw, and

c. said mating screw threads being so constituted as to provideclearance spaces therebetween whereby the screw can physically occupythe bore of the nut without contact between said threads,

d. said roller normally tending to maintain a spacing between saidthreads so as tokeep the same out of contact with each other.

3. The invention as set forth in claim 1, and further including: V

a. additional'rollers carried by said nut body and spaced about theinner periphery thereof,

b. bearing means mounting said additional rollers for turning movementabout their respective axes, and for movement between advanced andretracted positions, and v i c. yieldable means biasing said rollersinto their advanced positions for engagement with the screw thread.

4. The invention as set forth in claim 2, wherein:

a. the thread of the nutextends in opposite directions axially of saidroller.

5. The invention as set forth in claim 1, wherein:'

a. said shoulder comprises a multiturn helical thread which isinterrupted intermediate its length by said roller.

6. The invention as set forth in claim 1, wherein:

a. the roller has a tapered configuration at its thread engaging end,

b. said yieldable biasing means urging the roller in an advanceddirection radially inward of the nut body.

7. The invention as set forth in claim 6, wherein:

a. said yieldable biasing means comprises a bowed spring washer.

8. The invention as set forth in claim 5, and further including:

means for use with a screw comprising, in combination:

a. a follower member, b. a roller carried by said member and adapted forengagement with the thread of the screw,

c. bearing means mounting the roller on said member for turning movementabout its axis.

d. yieldable means for biasing the roller to an advanced position foreffecting engagement thereof with the screw thread, and

e. a shoulder rigid on said member and adapted for cooperable engagementwith a part of said thread,

f. said shoulder being arranged so it is normally out of engagement withthe thread when the roller is in said advanced position,

g. said yieldable biasing means enabling the roller to shift to aretracted position in response to heavy lateral loading thereon by thescrew, such that the shoulder of the member frictionally engages thescrew thread and effects an increased drag therewith, tending to retardrelative turning between the follower member and screw.

1. A variable efficiency nut for a screw comprising, in combination: a.an annular nut body having a through bore to receive the screw, b. aroller carried by said nut body and extending into the bore thereof soas to be engageable with the thread of the screw, c. bearing meansmounting the roller for turning movement about its axis, and formovement between advanced and retracted positions in the body, d.yieldable means biasing the roller to its advanced position forengagement with the thread of the screw, and e. a shoulder rigidlycarried in the bore of the nut body and engageable with a part of thescrew thread, f. said shoulder being normally out of engagement with thescrew thread when the roller is in its advanced position adapted toengage the thread, g. said yieldable biasing means enabling the rollerto yield and shift to its retracted position in response to heavylateral loading thereon by the screw, such that the shoulder of the nutbody frictionally engages the screw thread and effects an increased dragtherewith, thereby tending to retard relative turning between the nutbody and screw.
 2. The invention as defined in claim 1, and furtherincluding: a. a screw having a spiral thread with crests and grooves, b.said shoulder comprising a portion of a screw thread adapted to matewith the thread of said screw, and c. said mating screw threads being soconstituted as to provide clearance spaces therebetween whereby thescrew can physically occupy the bore of the nut without contact betweensaid threads, d. said roller normally tending to maintain a spacingbetween said threads so as to keep the same out of contact with eachother.
 3. The invention as set forth in claim 1, and further including:a. additional rollers carried by said nut body and spaced about theinner periphery thereof, b. bearing means mounting said additionalrollers for turning movement about their respective axes, and formovement between advanced and retracted positions, and c. yieldablemeans biasing said rollers into their advanced positions for engagementwith the screw thread.
 4. The invention as set forth in claim 2,wherein: a. the thread of the nut extends in opposite directions axiallyof said roller.
 5. The invention as set forth in claim 1, wherein: a.said shoulder comprises a multiturn helical thread which is interruptedintermediate its length by said roller.
 6. The invention as set forth inclaim 1, wherein: a. the roller has a tapered configuration at itsthread engaging end, b. said yieldable biasing means urging the rollerin an advanced direction radially inward of the nut body.
 7. Theinvention as set forth in claim 6, wherein: a. said yieldable biasingmeans comprises a bowed spring washer.
 8. The invention as set forth inclaim 5, and further including: a. a plurality of biased rollers movablebetween advanced and retracted positions and extending into the bore ofthe nut, said rollers being disposed along said multiturn helicalthread.
 9. The invention as set forth in claim 1, wherein: a. saidbearing means comprises a needle bearing engaging the lateral surface ofthe roller, and b. a ball thrust bearing disposed adjacent thenon-thread-engaging end of the roller.
 10. A variable efficiencymechanical transmission means for use with a screw comprising, incombination: a. a follower member, b. a roller carried by said memberand adapted for engagement with the thread of the screw, c. bearingmeans mounting the roller on said member for turning movement about itsaxis. d. yieldable means for biasing the roller to an advanced positionfor effecting engagement thereof with the screw thread, and e. ashoulder rigid on said member and adapted for cooperable engagement witha part of said thread, f. said shoulder being arranged so it is normallyout of engagement with the thread when the roller is in said advancedposition, g. said yieldable biasing means enabling the roller to shiftto a retracted position in response to heavy lateral loading thereon bythe screw, such that the shoulder of the member frictionally engages thescrew thread and effects an increased drag therewith, tending to retardrelative turning between the follower member and screw.